1. Field of Invention
This invention relates firstly to cementitious compositions of pozzolanic or geopolymeric type in their plastic state. Geopolymers are meant as compositions as taught by J Davidovits. Secondly, this invention relates to the plastic state compositions' resulting set and hardened compositions. Thirdly, this invention relates to methods of manufacturing both plastic state and hardened state compositions. In particular, the present invention relates to cementitious compositions of a type that may be brought to firstly foam or swell up while in an aqueous plastic state by a chemical foaming agent and also a process, and then secondly set into a hardened mass of hollow cells.
2. Prior Art
Well known methods of foaming a wet cementitious paste or slurry are by adding a gas generating chemical. Well known gas generating chemicals are those that react with an alkali, normally present in the cement slurry, to form hydrogen gas. Aluminium, zinc, or silicon powders are used to react with the alkaline environment present in the cement slurry to form hydrogen gas which causes foam bubbles in the slurry.
A difficulty in using such gas generating powders is that they must be well mixed in just prior to foam processing, since the foaming begins with powder addition and proceeds to completion without further control thereafter. Another difficulty arises when the foaming action is so overpowering as to render the ensuing composition fragile.
Various means of delayed action or slow release of foaming or setting have been proposed in order to design a retarded foaming or setting time. Foaming, retarding, or accelerating chemicals may be further coated by a barrier. Then in turn other chemicals, alone or in combination, attack the barrier coating to expose the underlying chemicals, whose action or reaction has now been delayed. However, although various process outcomes may be thus designed, these processes, once set in motion, are still subject to following along to a set designed outcome. In other words, the outcome cannot be controlled during the process, but is controlled by prior design before the process is activated.
When process control of a foaming and setting process is limited, then the applications of a manufacturing process and, in turn, its articles become limited. Thus it is desirable to have a process that may be retarded or accelerated according to feedback control by external means, such as by heating during the process, rather than by only following along a pre-designed process. This suggested process control, in turn, suggests the possibility of a more controlled process for the manufacturing of cementitious articles.
Fly ash collected from the flues of coal burning power stations is a waste by-product which accumulates around the world for want of wide-spread utilisation. Yet fly ash is a surprisingly well processed composition. Fly ash may be considered as burnt clay, which is already finely divided, homogenous and is chemically reactive with lime to form a type of cement which is termed pozzolanic cement. However, since this pozzolanic cement is, generally speaking, inferior to Portland cement, it is not utilised widely in a pure form, but rather as an additive in Portland cement or as a filler in other compositions. It is therefore desirable to utilise fly ash cement in applications that do not compete with Portland cement applications.
The most widespread applications of foamed and hardened cementitious compounds rely on a process that uses silica sand or Portland cement as its main feedstock ingredient. Silica sand is not a waste product and it requires further pulverising to bring it to a finely divided state suitable for the abovementioned process. It is preferably desirable to increase the utilisation of fly ash waste into useful articles than process silica sand to that end.
In the prior arts of special cement making, calcium hypochlorite has been suggested as an additive to cementitious and fly ash mixtures. However, the calcium hypochlorite is suggested to be used merely as an oxidant of other reactants, or coatings of reactants, in the mix. The reactants are typically impurities found in fly ash, such as sulphite. Another typical reactant is a specially prepared coating on reagent compositions, which coating is oxidised to then expose the reagent composition which may then in turn react in cement mixtures. The purpose of the abovementioned procedure is to gain some measure of process control of cement foaming or setting. This illustrates the trouble taken in the prior art to provide process control. This suggests the importance of foaming and setting process control in particular cement applications.
In the foaming of geopolymers, hydrogen peroxide and other peroxides have been used as foaming agents. Sodium perborate which provides peroxide during a breakdown stage has been suggested for foaming geopolymers. These foaming agents have been suggested for geopolymers manufactured with a component of soluble silicate.
3. Objects and Advantages
It is an object of an embodiment of the invention to provide a foaming agent useful in foaming pozzolanic and certain types of geopolymeric cementitious compositions. The foaming agent is suitable for a type of geopolymeric cementitious composition that does not require a soluble silicate component.
It is another object of an embodiment of the invention to provide an aqueous cementitious slurry that may be further activated to foam and then to set hard by applied heat into useful materials and articles of hardened cellular cementitious composition. This suggests extensive advantages for a production process, when a passive cementitious slurry may be kept in a hopper, handled, and placed in position before being activated by heating means controlled by an operator. In other words, the cementitious slurry may be kept wet in a plastic state and in a mixed and prepared form for a period of time without the foaming and setting process being activated. So the slurry may have a pot life of at least approximately an hour.
When manufacturing a large article that requires placing in stages over a large area, an advantage of having a substantial pot life is suggested in that the foaming may be delayed until all the stages are placed.
For manufacture by continuous process, an advantage of control of process is suggested. This parameter of control is that the amount of foaming and the amount of setting of the composition may be controlled during the process by an operator to some extent. The control of process is an improvement in that it is an external control means that may be applied according to data feedback received during the manufacturing process. This suggests that the control mechanism is then useful for producing quality articles.
An object of a further embodiment of the invention is to provide useful articles of hardened cellular cementitious composition. The suggested advantages are in providing articles with special combinations of useful physical attributes. Some of the desired attributes of the composition may be found in the following list of attributes: lightweight; rigid; high rigidity in relation to density; heat insulating; sound insulating; sound absorbing; fire-resistant; non-combustible; inexpensive; tough; strong; made from waste material; easy formed; easily shaped. Different sets of useful attributes are applicable for different applications.
Notable features of cellular cementitious composition of some embodiments of the invention are substantially evenly-sized thin-walled cells that are strong.
Still further objects of yet other embodiments of the invention are to provide methods of manufacture of aqueous cementitious slurry and of hardened cellular cementitious composition.